This report describes some properties of a certain class of
multi-way dataflow constraint systems with hierarchies. This class
arises in the implementation of property models, an approach that
enables a high level of reuse in programming user interfaces. We prove
that any solution of a constraint system in this class is unique,
define a class of changes in a constraint hierarchy that are
guaranteed to keep the solution of the constraint system unchanged, and
determine the extent to which other changes in a constraint hierarchy affect
the solution of the constraint system.